The invention relates to an electromagnetic wave switch formed from a semiconductor placed in a wave-guide and operating for millimeter waves. The object of such a device is to transmit certain micro-wave frequency signals and to attenuate others.
The prior art supplies examples of construction of micro-wave frequency switches, formed more particularly from a PIN diode associated with a biassing circuit and mounted in a wave-guide. FIG. 1 shows in cross section a rectangular wave-guide 1 comprising a PIN diode 2 placed on one of the internal faces 3 of the guide. The biassing voltage V for the diode is fed through a coaxial line 4 which is connected to the case of the diode through an micro-wave frequency trap 5 and a metal bar 6, the trap being separated from the coaxial line by a piece of insulation 50. The operation of such a switch is the following: when the diode is disabled, it is equivalent with its biassing circuit to a parallel resonating circuit, whereas when it is conducting, it is equivalent to a series resonating circuit, thus letting through the micro-wave frequency signal propagated in the wave-guide or attenuating it.
There exist another type of micro-wave frequency switch, related to the preceding one, and comprising a PIN diode. It operates in mode 2, that is to say that the PIN diode and its circuit present a series resonating circuit when the diode is disabled and a parallel resonating circuit when it is conducting.
Two main disadvantages appear during operation of this kind of switch. One is due to the fact that the cases protecting the PIN diodes as well as the different elements, such as the metal bar which provides both mechanical mounting and the bias input for the diode, are inductive or capacitive parasite elements limiting the operating pass-band of the switch.
The other disadvantage is due to the impossibility of using such a switch for millimeter waves. In fact, for the proper operation of the switch, a PIN diode is necessary having a very small junction capacity, which is very difficult to achieve and which may cause poor power behavior because of too low a breakdown voltage and/or a poor thermal resistance of the diode.